Question 122: EM waves

Question

A plane electromagnetic wave, has frequency
of 2.0 $$ 	imes $$ 1010 Hz and its energy density is
1.02 $$ 	imes $$ 10–8 J/m3 in vacuum. The amplitude of
the magnetic field of the wave is close
to
( $${1 \over {4\pi {\varepsilon _0}}} = 9 	imes {10^9}{{N{m^2}} \over {{C^2}}}$$ and speed of light =
3 $$ 	imes $$ 108 ms–1)

Accepted Answer

Energy density, $${{dU} \over {dV}} = {{B_0^2} \over {2{\mu _0}}}$$
$$ \Rightarrow $$ 1.02 $$ 	imes $$ 10
Ã¢ÂÂ8
= $${{B_0^2} \over {2{\mu _0}}}$$
Also, c = $${1 \over {\sqrt {{\mu _0}{\varepsilon _0}} }}$$
$$ \Rightarrow $$ $${\mu _0} = {1 \over {{c^2}{\varepsilon _0}}}$$
$$ 	herefore $$ $${B_0^2}$$ = 1.02 $$ 	imes $$ 10
Ã¢ÂÂ8
$$ 	imes $$ 2 $$ 	imes $$ $${1 \over {{c^2}{\varepsilon _0}}}$$
= 1.02 $$ 	imes $$ 10
Ã¢ÂÂ8
$$ 	imes $$ 2 $$ 	imes $$ $${{4\pi  	imes 9 	imes {{10}^9}} \over {9 	imes {{10}^{16}}}}$$
$$ \Rightarrow $$ B
0
= 16 $$ 	imes $$ 10
-8
T = 160 nT

Answer

190 nT

Answer

150 nT

Answer

160 nT

Answer

180 nT

EM waves

Choose the correct answer: